could not create merged face
Instead of creating new faces I used the merge vertices function of blender, here's the final result: 
 
I noticed where the leg of the turtle meets the body of the turtle they are not connected. 
 
All the vertices looked like the second vertex down, on both sides. 

How to fix 

First of all go to where the right leg and body meet, in edit mode. 
From their select one vertex attached to the body. Then select the corresponding vertex on the leg like this: 
 
Once there press Alt + M and finally press A. Once completed do the same to all the vertices, on both sides of the leg. 
If you play the animation now the leg will be deformed, to fix this simply re-set the parent of the mesh to the armature. I did this using automatic weights. 

Happy Blendering!